Absorption Spectra and Structure of Barbituric Acid Derivatives as a Function of pH

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Abstract
Summary.‐ The ultraviolet absorption spectra of several barbituric acid derivatives have been measured and their apparent dissociation constants determined.The variation of the spectra of barbital and its N‐methyl derivatives with pH is shown to be explicable on the basis of ionic dissociation.The spectrum of barbituric acid, in which only two of the three potentially‐dissociable groups are exhibited, is discussed in relation to other spectral characteristics.The sites of enolizations in barbituric acid and barbital and the order in which these ionic equilibria occur as a function of pH are suggested.